Conveyance of electrically charged sheets

ABSTRACT

An electrophotographic apparatus wherein charged sheets are conveyed from a liquid developer to a dryer by a pair of rollers of insulating material, suitably polyurethane. Each of these insular rollers is engaged by a stainless steel roller which is maintained at a predetermined electrical potential and thereby reduces the amount of electrical charge, picked up by the associated insulating roller, which is returned to a subsequent part of the sheet. The stainless steel rollers may be maintained at a high potential of the same polarity of the toner particles used in the developer, in which case there is a reduction in the number of particles, picked up by the insulating rollers, which is returned to the sheet.

United States Patent [72] inventor Martin R. P. Seib l0, Lodge Drive, The Ryde, Hatfield, l'lertl'ordshire, England 121 1 Appl. No. 753,297 [22] Filed Aug. 16, 1968 [45] Patented Feb. 2, 1971 [54] CONVEYANCE 0F ELECTRICALLY CHARGED SHEETS 3 Claims, 1 Drawing Fig.

[52] US. Cl 118/637, 1 l 7/3 7 [51 Int. Cl 1305b 5/02 [50] Field oiSearch 118/637, 639:117/175, 37LX [56] References Cited UNITED STATES PATENTS 3,155,546 11/1964 Dirks 118/637 3,345,925 10/1967 Ostensen 3,202,526 8/1965 Ostensen Primary Examiner-Peter Feldman Attorney-Delio and Montgomery ABSTRACT: An electrophotographic apparatus wherein charged sheets are conveyed from a liquid developer to a dryer by a pair of rollers of insulating material, suitably polyurethane. Each of these insular rollers is engaged by a stainless steel roller which is maintained at a predetermined electrical potential and thereby reduces the amount of electrical charge,

picked up by the associated insulating roller, which is returned to a subsequent part of the sheet. The stainless steel rollers may be maintained at a high potential of the same polarity of the toner particles used in the developer, in which case there is a reduction in the number of particles, picked up by the insulating rollers, which is returned to the sheet.

CONVEYANCE OF ELECTRICALLY CHARGED SHEETS BACKGROUN D OF THE INVENTION This invention relates to conveying means for electrically charged sheets of electrophotographic paper.

In electrostatic developing and printing apparatus an electrostatic charge is formed in a photoconductive layer on one surface of an electrophotographic paper and an optical image of apredetermined object is focused on to the charged surface by optical projection means. The charge leaks away from those areas of the charged surface which are subjected to electromagnetic radiation and an electrostatic charge image, corresponding to the photographic image projected by the optical projection means, is thereby formed. To develop the electrostatic image the sheet is suitably passed through a developing bath containing a liquid suspension of black, charged toner particles in an insulating liquid such as paraffin. The charged particles adhere to the charged or uncharged areas of the sheet, according to their polarity, and thereby produce a positive or negative print of the original photographic image. Fixing is effected by drying the sheet to remove excess paraffin.

In electrostatic apparatus of the above form it is important that the charge distribution on a sheet shall not be distributed during transport of a sheet from the developing means to drying of fixing means.

SUMMARY OF THE INVENTION The present invention consists in means for conveying a charged sheet of electrophotographic paper from liquid developer means to drying means comprising cooperating driving elements which are adapted to engage respective opposite sides of the sheet and, in driving the sheet along a predetermined path, to remove liquid developer therefrom, each driving element having the sheet engaging surface thereof formed of electrically insulating material, wherein the driving element which engages a photoconductive layer of the sheet is engaged at a location spaced from the path of the sheet by an electrically conductive element, and means are provided for maintaining the electrically conductive element at a predetermined electrical potential, whereby the electrically conductive element reduces the amount of electrical charge, transferred to the associated driving element from the charged sheet, which is transferred back from the driving element to a part of the sheet subsequently engaged by the driving elements.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawing which is a side elevation of conveying means to the invention.

The conveying means shown in the drawing form part of an electrophotographic apparatus which includes a store for sheets of electrophotographic paper, means for dispensing sheets individually from the store to a charger in which a charge is induced in a photoconductive layer of the sheet, and driving means 1 for conveying sheets from the charger to a viewing table 3. On the table 3 a sheet is exposed to light from an optical projection system of the apparatus and an electrostatic image is formed on the charged photoconductive layer. After exposure the driving means 1 convey the sheet to a liquid developer 5 and from the developer the sheet is driven by conveying means 7 to fixing and drying means 9. I

As indicated in the drawing, the table 3 is upwardly and rearwardly inclined from front to rear of the apparatus, from right to left as seen in the drawing. The driving means 1 are mounted on the table 3 and include an upper driving roller 10 and a series of endless belts 11 which engage the roller 1 and further rollers, not shown in the drawing, and which have their upper runs in flatwise engagement with the top of the table.

An exposed sheet of paper is engaged between the belts 11 and a guide sheet 13 of polytetrafluorethylene as it leaves the table 3 and is directed downwardly to a developer tray 15 of the above-mentioned developer 5. The tray 15 is arcuate in section and has the base thereof formed with upstanding ribs 17. A liquid suspension of black, positively charged toner par ticles in paraffin is pumped from a tank (not shown) to a spray bar 19 above the tray 15, from which the liquid is directed on to a sheet entering the tray. Excess liquid is continuously decanted from the tray 15 to the tank.

On the outlet side of the tray 15 are the conveying means 7 for driving a sheet from the tray to the fixing and drying means 9.

The conveying means 7 include a series of four rollers 21, 23, 25 and 27 each of which is journaled at opposed ends thereof in respective mounting plates 29. Mounting plates 29 are secured to a shaft 31 which extends parallel to the axes of rollers 21 to 27 and rests in slots 33 in respective supporting brackets 35.

One end of the roller 23 is coupled via a clutch mechanism (not shown) to a chain 37 which is driven by an electric motor (also not shown). The conveying means 7 can therefore be removed from the apparatus to provide access to the tray 15 by releasing the clutch mechanism and lifting the shaft 31 out of the slots 33.

Each of the rollers 23 and 25 consists of a metal spindle which extends between the mounting plates 29 and is provided with a covering of polyurethane over a major part of its length. A sheet of electrophotographic paper emerging from the tray 15 is engaged between rollers 23 and 25 and is driven thereby to the fixing and drying means 9.

Roller 21 is disposed vertically above the roller 23 and engages the latter at a location spaced from the path of a sheet from the tray 15 and diametrically opposed to the location at which roller 23 is engaged by roller 25. Roller 27 is disposed vertically beneath the roller 25 and engages roller 25 at a location diametrically opposed to its engagement with roller 23. Each of the rollers 21 and 27 is formed of stainless steel and is maintained at earth potential by virtue of the electrically conductive connection which extends via the bearings for the roller, mounting plates 29 and the brackets 35 to the earthed framework of the apparatus.

In use of the apparatus, an electrostatic image is formed in a photoconductive layer of a sheet on the table 3 and the driving means 1 are then energized to drive the sheet downwardly towards the tray 15. The leading edge of the sheet engages the ribs 17 on the base of the tray and is guided downwardly and rearwardly of the apparatus, into the liquid developer, and then upwardly and rearwardly towards the rollers 23 and 25. During its passage through the tray an electrically conductive base layer of the sheet is supported in the ribs 17.

Within the tray 15 black, positively charged toner particles adhere to the charged or uncharged areas of the photoconductive layer of the sheet, according to the polarity of the charges induced by the charger. A certain amount of a parafiin is also drawn from the tray 15 by the sheet.

In passing between the polyurethane rollers 23 and 25 at the outlet side of the tray 15 some of the paraffin is squeezed from the sheet, and further drying is effected by the fixing and drying means 9. At the same time, however, electrostatic charge and black toner particles are transferred from the sheet to the rollers 23 and 25 and in the absence of the stainless steel rollers 21 and 27 an electrical image and toner particles would be reprinted on a subsequent section of the sheet by the rotation of rollers 23 and 25.

By maintaining the rollers 21 and 27 at earth potential the electrical charge transferred from the sheet to the rollers 23 and 25 is conducted away and *reprinting" of the electrical image is therefore prevented.

By applying a high positive potential (up to 1000 volts) to the stainless steel rollers 21 and 27 the positively charged toner particles are repelled and, accordingly, prevented from being carried round by the driving rollers 23 and 25 and deposited on subsequent sections of the charged sheet. This keeps both sides of the paper clean, which is important if the sheet is subsequently used for printing on to other materials.

I claim:

1. Means for conveying a charged sheet of electrophotographic paper from liquid developer means to drying mcans comprising cooperating driving rollers which are adapted to engage respective opposite sides of the sheet and. in driving the sheet along a predetermined path, to remove liquid developer therefrom, each driving roller having the sheet engaging surface thereofformed of electrically insulating material. each driving roller which engages a photoconductive layer of the sheet being engaged at a location spaced from the path of the sheet by an electrically conductive roller, and means for maintaining the electrically conductive rollers at a predetermined electrical potential, whereby the electrically conductive roller reduces the amount of electrical charge, transferred to the associated driving roller from the charged sheet, which 5 is transferred back from the driving roller to a part of the sheet subsequently engaged by the driving rollers.

2. Conveying means as claimed in claim 1, wherein means are provided for maintaining the or each electrically conductive roller at earth potential.

3. Conveying means as claimed in claim I, wherein means are provided for maintaining the or each electrically conductive roller at a high electrical potential of the same polarity as the polarity of the toner particles on the sheet, whereby there is a reduction in the number of toner particles, transferred to the or each associated driving roller from the charged sheet, which are transferred back to a part of the sheet subsequently engaged by the driving rollers. 

1. Means for conveying a charged sheet of electrophotographic paper from liquid developer means to drying means comprising cooperating driving rollers which are adapted to engage respective opposite sides of the sheet and, in driving the sheet along a predetermined path, to remove liquid developer therefrom, each driving roller having the sheet engaging surface thereof formed of electrically insulating material, each driving roller which engages a photoconductive layer of the sheet being engaged at a location spaced from the path of the sheet by an electrically conductive roller, and means for maintaining the electrically conductive rollers at a predetermined electrical potential, whereby the electrically conductive roller reduces the amount of electrical charge, transferred to the associated driving roller from the charged sheet, which is transferred back from the driving roller to a part of the sheet subsequently engaged by the driving rollers.
 2. Conveying means as claimed in claim 1, wherein means are provided for maintaining the or each electrically conductive roller at earth potential.
 3. Conveying means as claimed in claim 1, wherein means are provided for maintaining the or each electrically conductive roller at a high electrical potential of the same polarity as the polarity of the toner particles on the sheet, whereby there is a reduction in the number of toner particles, transferred to the or each associated driving roller from the charged sheet, which are transferred back to a part of the sheet subsequently engaged by the driving rollers. 